Definition Quantum Dot Lasers can be considered as a quantum leap in the development
of lasers. Quantum Dots improve basically the laser emissions. This property of
Quantum Dots is well utilized for fiber optic communication, which is now the
leading subject under research and development. Quantum Dots are thus very well
used in applications fiber optic communication. The remaining major division of
the field of quantum electronics deals with the interactions of coherent light
with matter and again leads to a wide range of all-optical and optoelectronic
devices.
Basically Quantum Dots are made of
InGaAs or simply GaAs structures. Also the possibility for extended wave length
(>1.1µm) emission from GaAs based devices is an important characteristic
of Quantum Dots. The QDs are formed by an optimized growth approach of alternating
sub-monolayer deposition of column III and column V, constituents for optoelectronic
device fabrication. Thus there is a large energy separation between states.The
infrastructure of the Information Age has to date relied upon advances in microelectronics
to produce integrated circuits that continually become smaller, better, and less
expensive. The emergence of photonics, where light rather than electricity is
manipulated, is posed to further advance the Information Age. Central to the photonic
revolution is the development of miniature light sources such as the Quantum dots(QDs).
Today, Quantum Dots manufacturing has been
established to serve new datacom and telecom markets. Recent progress in microcavity
physics, new materials, and fabrication technologies has enabled a new generation
of high performance QDs. This presentation will review commercial QDs and their
applications as well as discuss recent research, including new device structures
such as composite resonators and photonic crystals Semiconductor lasers are key
components in a host of widely used technological products, including compact
disk players and laser printers, and they will play critical roles in optical
communication schemes. The basis of laser operation depends on the creation of
non-equilibrium populations of electrons and holes, and coupling of electrons
and holes to an optical field, which will stimulate radiative emission. . Other
benefits of quantum dot active layers include further reduction in threshold currents
and an increase in differential gain-that is, more efficient laser operation.
Since the 1994 demonstration of a quantum
dot (QD) semiconductor laser, the research progress in developing lasers based
on QDs has been impressive. Because of their fundamentally different physics that
stem from zero-dimensional electronic states, QD lasers now surpass the established
planar quantum well laser technology in several respects. These include their
minimum threshold current density, the threshold dependence on temperature, and
range of wavelengths obtainable in given strained layer material systems. Self-organized
QDs are formed from strained-layer epitaxy. Upon reaching such conditions, the
growth front can spontaneously reorganize to form 3-dimensional islands. The greater
strain relief provided by the 3-dimensionally structured crystal surface prevents
the formation of dislocations. When covered with additional epitaxy, the coherently
strained islands form the QDs that trap and isolate individual electron-hole pairs
to create efficient light emitters.
Optimizing
the QD characteristics for use as practical, commercial light sources is based
on controlling their density, shape, and uniformity during epitaxy. In particular,
the QD's shape plays a large role in determining its dynamic response, as well
as the temperature sensitivity of the laser's characteristics. Their density,
shape, and uniformity also establish the optical gain of a QD ensemble. All three
physical characteristics can be engineered through the precise deposition conditions
in which temperature, growth rate, and material composition are carefully controlled.